Highly Anisotropic Piezoelectric Ceramics and Their Application in Ultrasonic Probes

Abstract

New piezoelectric ceramics with extremely large electromechanical anisotropies are reviewed. They are modified lead titanate ceramics (Pb.Sm) (Ti,Mn)Oj and (Pb,Ca)(Ti,(Col/ 2W1/2)03 +MnO.NiO and lead zirconate ceramics modified by adding small amounts of Pb(CERAmnl/3 Nb2/3 )O3 and PbTiOj. In these ceramics, the planar electromechanical coupling factor kp is much less than the thickness dilatational electromechanical coupling factor kt (kt/kp >lo). These ceramics are especially useful for use in high-frequency array transducers. In contrast to ordinary ceramics such as PZT, the width-to-thickness ratio of a transducer element (w/t) can be larger than unity. The features of a high-frequency linear array and of single element ultrasonic probes employing modified lead titanate ceramics are also described.